Devices for photographically monitoring road intersections controlled by traffic lights are known (German Auslegeschrift No. 1,078,797). Such devices shall detect vehicles entering the road intersection during the stop phase in a manner able to identify them. To this end a sensor in the form of an induction loop is imbedded in the road carpet of the monitored road just before the junction with the road intersection. The sensor responds to a vehicle driven thereover and supplies a sensor signal. A further signal is received at the traffic light when the traffic light changes to the stop phase. A photographic camera is released by a control and evaluation unit when a sensor signal occurs during the stop phase, which is the case when a vehicle enters the road intersection during the stop phase. The camera supplies a picture in which the vehicle in the road intersection and the traffic light showing "red" can be seen. In the picture also the licence number can be seen such that the vehicle can be identified. In order to increase the evidential value several pictures are usually taken one after the other at fixed time intervals (German Pat. No. 2,365,331).
These devices do not just serve to determine violation of traffic regulations but they also act to prevent such violations. To this end, devices for red light monitoring have to be installed in the municipal area at a number of road intersections controlled by traffic lights. This would be very expensive for the installation of the devices as well as for the evaluation of the pictures taken therewith. For this reason, traffic monitoring devices are often made of two parts: They have components fixedly installed at the operation site and an insert adapted to be inserted at different places of operation. The stationary components fixedly installed are the sensor imbedded in the road carpet and a housing usually arranged on a support, the sensor being connected to plugs in the housing through fixedly imbedded lines. The insert comprises the photographic camera, a flash device, and a control and evaluation unit which controls the course of operation and couples the signals obtained from the sensor and from the traffic light for releasing or not releasing the camera. Therewith, at different places of operation, an insert can be inserted for random periods of time in the housing in question. Then the car driver does not know in which housing an insert having camera, flash device, and control and evaluation unit is inserted, i.e. which device is in operation.
There are often different conditions at the different places of operation. These conditions have to be taken into account in the course of operation of the device. The "yellow phases" before the stop phases "red" can, for example, have different durations. The spatial dimensions of road intersections and the position of the sensors relative to the road intersections can be different, which requires different regulations of the delay times for different places of operation. For the purpose of registration, an identification sign or a designation of the operation site has to be input on or with the pictures. Furthermore, in many cases, the operation site has particular characteristics. The position of the sun, for example, can be disadvantageous at certain moments, such that it is not possible to take any useful pictures. In this case it is necessary to switch-off the device during this period of time in order to avoid an unnecessary film consumption. To this end, possibilities of adjustment are provided at devices for monitoring road intersections controlled by traffic lights. By means of these possibilities of adjustment, the police officer manually inputs the parameters specific for the operation site in question.
Where such a manual input is involved, it requires special attention. Therefore the risk of incorrect input of the data is present. Incorrect input of the data reduces the evidential value of the picture. Incorrect input of the switch-off moments leads to unnecessary film consumption and reduces the duration of operation, during which, in fact, monitoring takes place. Furthermore, speed monitoring devices operating with Doppler radar are known. With these devices a radar beam is generated by means of a radar antenna. The speed of the vehicle is determined from the frequency shift obtained due to the Doppler effect when the radar beam is reflected from a moving vehicle. The speed thus determined is compared with a predetermined maximum speed limit. If this maximum speed limit is exceeded, a camera is released and a picture of the vehicle is taken permitting identification of the vehicle (Swiss Pat. No. 414,210).
Also such speed monitoring devices are often used "stationarily" at well determined places of operation. Also herein it is known to fixedly install housings at these places of operation, for example at bridge constructions over expressways, and to form the actual measuring device with the camera and the control as an insert adapted to be optionally inserted into different housings. Also herein it is necessary to adjust at the device the parameters specific for the operation site in question. In particular, the maximum speed limit predetermined at the operation site is one of these parameters.
Furthermore, integrated devices are known having a camera and a control and evaluation unit, which are arranged to be optionally applied for monitoring road intersections controlled by traffic lights and for speed monitoring in fixedly installed housings. In this case, a program specific for the desired mode of operation has to be input in the control and evaluation unit.